The invention relates to a tubular element for use in a rotary drilling assembly.
Rotary drilling assemblies used in underground well drilling operations generally comprise a drill bit connected at the lower end of an elongate drill string. The drilling assembly may comprise a downhole drilling motor which drives the bit while the drill string above the motor is not rotated or rotated slowly by the rotary table at the surface.
As disclosed in European patent specifications No. 85444 and 109699, which correspond to U.S. Pat. Nos. 4,465,147 and 4,492,276, respectively, it may be desired that the drill string is not rotated during at least part of the drilling operations so as to maintain the tool face of the bit in a predetermined tilted orientation in the borehole in order to drill a deviated hole section. A difficulty encountered during such oriented drilling operations is that weight on bit fluctuations generate reactive torque fluctuations as a result of which the amount of twist in the elongated drill string varies and the orientation of the tool face becomes unstable. This unstable tool face orientation makes the steering process less effective and difficult to control. Thus there is a need for a drilling assembly which can be prevented from making swinging motions in the borehole as a result of reactive torque fluctuations.